Effect of encapsulating agents on dispersion status and photochemical reactivity of C60 in the aqueous phase

Hand-ground fullerene-nanodiamond composite for photosensitized water treatment and photodynamic cancer therapy

The unique capability of fullerene (C₆₀) to absorb light and generate reactive oxygen species (ROS) has been extensively studied for photosensitized water treatment and cancer therapy. Various material synthesis strategies have been proposed in parallel to overcome its intrinsic hydrophobicity and to enhance availability in water and physiological media. We present here a strikingly simple approach to make C₆₀ available to these applications by hand-grinding dry C₆₀ powder with nanodiamond (ND) using a mortar and pestle. The resulting ND-C₆₀ composite was found to form a stable aqueous colloidal suspension and efficiently drive photosensitized production of ROS under visible light illumination. ND-C₆₀ rapidly adsorbed and oxidized organic contaminants by photogenerated ROS. In the experiments for photodynamic cancer therapy, ND-C₆₀ was internalized by cancer cells and induced cell apoptosis without noticeable toxicity. Treatment of tumor-bearing mice with ND-C₆₀ and light irradiation resulted in tumor shrinkage and prolonged survival time.

Magnetic Fullerene-DNA/Hyaluronic Acid Nanovehicles with Magnetism/Reduction Dual-Responsive Triggered Release

We created the dual-responsive nanovehicle that can effectively combine and abundantly utilize magnetic and glutathione (GSH)-reductive triggers to control the drug delivery and achieve more intelligent and powerful targeting. In the nanovehicles, paramagnetic fullerene (C₆₀@CTAF) was prepared via one-step modification of fullerene with magnetic surfactant CTAF by hydrophobic interaction for the first time. The perfect conjugation of C₆₀ and CTAF increased the solubility or dispersity of fullerenes and qualified CTAF with more powerful assembly capability with DNA. DNA molecule in the nanovehicles acted as an electrostatic scaffold to load anticancer drug Dox as well as the important building block for assembly with C₆₀@CTAF into C₆₀@CTAF/DNA. The further combination of deshielding and targeting functions in reduction-responsive disulfide modified HA-SS-COOH coating on C₆₀@CTAF/DNA complexes could reduce the agglomeration and regulate the morphology of C₆₀@CTAF/DNA complexes from irregular microstructures to more uniform ones. More importantly, the introduction of HA-SS-COOH provided a response to a simulating reductive extra-tumoral environment by efficient cleavage of disulfide linkages by GSH and site-specific drug delivery to HepG2 cells. Amazingly, the final nanovehicles presented an increased magnetic susceptibility compared with paramagnetic CTAF, and they "walked" under an applied magnetic field. Because of their facile fabrication, rapid responsiveness to extra tumoral environment, and external automatic controllability by external magnet, the drug delivery nanovehicles constructed by magnetic fullerene-DNA/hyaluronic acid might be of great interest for making new functional nucleic-acid-based drug carriers.

Fate of radiolabeled C60 fullerenes in aged soils

Fullerenes (e.g. C₆₀, C₇₀, etc.) present in soil may undergo changes in its retention with aging. In this study, the partitioning behavior of (¹⁴C)-C₆₀ aged up to 12 weeks was investigated in biosolids-amended soil. Spiked samples were subjected to sequential partitioning using water, methanol, and toluene followed by total combustion of solids; the distribution of ¹⁴C across solvents and matrices were used to provide insights on C₆₀ behavior. In most samples, ¹⁴C only partitioned in toluene with the remaining (non-extractable) activity detected in the solid phase. In all biosolids-amended soil samples, an increase in non-extractable ¹⁴C were observed for those exposed to light (vs dark) with the greatest difference observed in biosolids + sand samples. Possible processes that contribute to the observed ¹⁴C distribution, i.e. retention and potential transformation of C_60, were discussed. Over-all, results suggest that environmental exposure to C₆₀ and potentially transformed C₆₀ species, as a result of their release from soils, is likely to be low.

Photochemical reactivity of aqueous fullerene clusters: C60 versus C70

Over the past few years, there has been a strong interest in exploring the potential impact of fullerenes in the environment. Despite that both C₆₀ and C₇₀ have been detected in environmental matrices, the research on the impact of higher fullerenes, such as C_70, has been largely missing. This study evaluated and compared the phototransformation of aqueous C₆₀ and C₇₀ clusters (nC₆₀ and nC₇₀) and their ¹O₂ production under sunlight and lamp light irradiation (315nm, 360nm and 420nm). The nC₆₀ and nC₇₀ samples formed by direct mixing with water adopted a face-centered cubic (FCC) crystal structure. The apparent quantum yields (AQYs) of fullerene phototransformed were relatively constant over the examined wavelengths, while ¹O₂ production AQYs decreased with increased wavelengths. The long-term fate studies with outdoor sunlight indicated that both nC₆₀ and nC₇₀ lost considerable organic carbon contents (>80%) in water after ∼8 months of irradiation and that the intermediate photoproducts of nC₆₀ and nC₇₀ exhibited a progressively increased level of oxygen-containing functionalities. Overall, the study indicates that nC₇₀ can be photochemically removed under sunlight conditions and that the photoreactivity of nC₆₀ based on AQYs is greater than that of nC₇₀.

Bioavailability of Fullerene under Environmentally Relevant Conditions: Effects of Humic Acid and Fetal Bovine Serum on Accumulation in Lipid Bilayers and Cellular Uptake

Carbon fullerene (C60) has emerged at the forefront of nanoscale research and application due to its unique properties. As the production of this nanoparticle rapidly increases, it can be released into natural aquatic environments and can accumulate in biological systems. This research examined the effects of humic acid and fetal bovine serum (FBS), which are ubiquitous in aquatic environments and representative of blood plasma in living organisms, respectively, on bioavailability of fullerene. Bioavailability was investigated using in vitro methods for lipid membrane accumulation and cellular uptake studies. Humic acid and FBS significantly changed the characteristics of fullerene including its particle size and surface charge. The effects of humic acid on lipid accumulation of fullerene depended on the lipid head charge. FBS also significantly decreased the lipid accumulation when positively charged and zwitterionic head groups were present on the lipids, possibly due to the higher steric repulsion of the protein coated nanoparticles. In addition, both humic acid and FBS protein effectively lowered the amounts of fullerene taken up by Caco-2 cells, which are derived from a human colorectal adenocarcinoma and have similar functions to the small intestinal epithelium. Results of this study suggest that surface modification of fullerene by environmentally relevant matrices can significantly affect the biological transport, as well as the possible toxicity of this nanomaterial.

Effect of surfactants on the removal and acute toxicity of aqueous nC60 aggregates in water treatment process

This work aimed to evaluate the effect of surfactants on the removal of aqueous nC60 aggregates by coagulation-filtration process and assess the acute toxicity of filtrates by Microtox test. Three surfactants including cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS), and Triton X-100 (TX100) were selected representing cationic, anionic, and nonionic types, respectively. Results showed that the change of physicochemical properties of nC60 associating with different types of surfactants determined nC60's removal efficiency and acute toxicity. CTAB increased the number of large particles. It also changed the zeta potential of nC60 from negative to positive, leading to the low removal rates (17.3-50.2%) when CTAB concentration was designed in the range of 0.03-1 g/L, and the filtrates showed acute toxicity to bioluminescent bacteria (inhibition rate > 80%). On the contrary, TX100 obviously increased the proportion of small particles, and it is noteworthy that even less than 1 mg/L of nC60 (20% of the initial concentration) with TX100 remaining in filtrates could evoke phototoxicity due to reactive oxygen species (ROS) generation under UV irradiation. Compared to CTAB and TX100, SDS exerted an effect on the removal process and toxicity of nC60 only when concentration was beyond the critical micelle concentration (CMC; 2.5 g/L). These findings collectively suggest that characteristics of nC60 are flexible and strongly dependent on surfactant modification, as a result of which these particles could potentially find their way through water treatment route and exert a potential toxicity risk.

Differential photoactivity of aqueous [C60] and [C70] fullerene aggregates

Many past studies have focused on the aqueous photochemical properties of colloidal suspensions of C60 and various [C60] fullerene derivatives, yet few have investigated the photochemistry of other larger cage fullerene species (e.g., C70, C74, C84, etc.) in water. This is a critical knowledge gap because these larger fullerenes may exhibit different properties compared to C60, including increased visible light absorption, altered energy level structures, and variable cage geometries, which may greatly affect aggregate properties and resulting aqueous photoactivity. Herein, we take the first steps toward a detailed investigation of the aqueous photochemistry of larger cage fullerene species, by focusing on [C70] fullerene. We find that aqueous suspensions of C60 and C70, nC60 and nC70, respectively, exhibit many similar physicochemical properties, yet nC70 appears to be significantly more photoactive than nC60. Studies are conducted to elucidate the mechanism behind nC70's superior (1)O2 generation, including the measurement of (1)O2 production as a function of incident excitation wavelength, analysis of X-ray diffraction data to determine crystal packing arrangements, and the excited state dynamics of aggregate fullerene species via transient absorption spectroscopy.

Functionalized fullerenes in water: a closer look

The excellent photophysical properties of C60 fullerenes have spurred much research on their application to aqueous systems for biological and environmental applications. Spontaneous aggregation of C60 in water and the consequent diminution of photoactivity present a significant challenge to aqueous applications. The mechanisms driving the reduction of photoactivity in fullerene aggregates and the effects of functionalization on these processes, however, are not well understood. Here, we take a closer look at the molecular phenomena of functionalized fullerene interactions in water utilizing simulation and experimental tools. Molecular dynamic simulations were performed to investigate time-evolved molecular interactions in systems containing fullerenes with water, oxygen, and/or neighboring fullerene molecules, complimented by physical and chemical characterizations of the fullerenes pre- and postaggregation. Aggregates with widely different photoactivities exhibit similar fullerene-water interactions as well as surface and aggregation characteristics. Photoactive fullerene aggregates had weaker fullerene-fullerene and fullerene-O2 interactions, suggesting the importance of molecular interactions in the sensitization route.

Interaction of C₆₀ with water: first-principles modeling and environmental implications

The nature of fullerene-water interactions has been the subject of much research and debate. Specifically, the presence of a stabilizing, negative surface potential on colloidal aggregates of C60 in water is unexpected, given the neutral nature of pure carbon, and is not well understood. Previous simulation efforts have focused on the C60-water interaction using molecular dynamics simulations that lacked the ability to account for charge transfer and distribution interactions. In this study, first-principles density functional theory was used to analyze the fundamental electronic interactions to elucidate the polarization and charge transfer between water and C60. Simulations show that charge is inductively transferred to the C60 from water molecules, with subsequent polarization of the C60 molecule. In a case with two neighboring C60 molecules, the charge polarization induces a charge onto the second C60. Simulation suggests that this charge transfer and polarization may contribute at least partly to the observed negative surface potential of fullerene aggregates and, combined with hydrogen bonding network formation around C60, provides a fundamental driving force for aggregate formation in water.

Reduction of hydroxylated fullerene (fullerol) in water by zinc: reaction and hemiketal product characterization

Water-soluble, hydroxylated fullerene (fullerol) materials have recently gained increasing attention as they have been identified as the primary product(s) during the exposure of fullerenes (as water stable, nanoscale aggregated C60) to UV light in water. The physical properties and chemical reactivity of resulting fullerols, however, have not been thoroughly studied. In this paper, we identified and characterized the reductive transformation of fullerol (C60(OH)x(ONa)y) by solid zinc metal (Zn(0)) through a series of batch reaction experiments and product characterization, including (13)C NMR, FTIR, XPS, UV-vis, DLS, and TEM. Results indicated the facile formation of water stable, pH sensitive hemiketal functionality as part of a relatively reduced fullerol product. Further, aqueous physical behavior of the product fullerol, as measured by octanol partitioning and surface deposition rates, was observed to significantly differ from the parent material and is consistent with a relative increase in molecular (product) hydrophobicity.

Effects of the preparation method and humic-acid modification on the mobility and contaminant-mobilizing capability of fullerene nanoparticles (nC60)

Colloidal fullerene nanoparticles (nC60) in aquatic environments may significantly affect the transport and risks of hydrophobic organic contaminants by serving as a contaminant carrier. The objective of this study was to understand how the combined variables of the preparation method and natural organic matter modification of nC60 might affect the mobility and contaminant-mobilizing capability of nC60, by affecting the physicochemical properties of nC60. We found that an nC60 sample prepared by sonicating C60 powder in deionized water (son_nC60) was much less mobile in saturated sandy soil columns than an nC60 sample prepared by solvent-exchanging from toluene to water (tol_nC60), because son_nC60 was considerably larger in size. However, son_nC60 exhibited greater capability to bind 2,2',5,5'-polychlorinated biphenyl (PCB), likely because its loosely packed structures rendered more pore spaces, which were favorable adsorption sites for PCB. Forming nC60 samples in Suwannee River humic acid (SRHA) solution (instead of deionized water) only moderately affected the mobility of nC60, but had very significant effects on the contaminant-binding capability of nC60, especially when nC60 was prepared using the solvent exchange method. Adding SRHA after the formation of nC60 had varied effects on the mobility and contaminant-binding capability of nC60, but the fundamental mechanism seems to be linked to how and to what extent SRHA had affected the aggregation/packing of C60 monomers. An important environmental implication is that nC60 formed under different environmental conditions might have vastly different effects on contaminant transport and risks.

Simple synthetic method toward solid supported c60 visible light-activated photocatalysts

Solid supported fullerene materials are prepared in aims of creating a fullerene-based photocatalyst that is capable of producing (1)O2 in the aqueous phase. Past studies of using fullerene as a photocatalyst in water have exclusively focused on using water soluble fullerene derivatives and employed sophisticated chemistry to create immobilized fullerene materials. The method presented herein is much less synthetically complex and utilizes pristine fullerene, providing a drastically simpler route to supported fullerene materials and furthering their potential for use in environmental applications. Covalent immobilization was achieved through the nucleophilic addition of a terminal amine (located on a solid support) across a [6,6] fullerene double bond, resulting in attachment directly to C60's cage. Immobilization allowed supported fullerene moieties to produce (1)O2 in water under various illumination conditions and inactivate MS2 bacteriophages. In a water with natural organic matter, supported fullerene materials produced (1)O2 under visible light irradiation without exhibiting significant loss of photocatalytic activity after successive cycling.

Photochemical transformation of carboxylated multiwalled carbon nanotubes: role of reactive oxygen species

The study investigated the photochemical transformation of carboxylated multiwalled carbon nanotubes (COOH-MWCNTs), an important environmental process affecting their physicochemical characteristics and hence fate and transport. UVA irradiation removed carboxyl groups from COOH-MWCNT surface while creating other oxygen-containing functional groups with an overall decrease in total surface oxygen content. This was attributed to reactions with photogenerated reactive oxygen species (ROS). COOH-MWCNTs generated singlet oxygen ((1)O2) and hydroxyl radical ((•)OH) under UVA light, which exhibited different reactivity toward the COOH-MWCNT surface. Inhibition experiments that isolate the effects of (•)OH and (1)O2 as well as experiments using externally generated (•)OH and (1)O2 separately revealed that (•)OH played an important role in the photochemical transformation of COOH-MWCNTs under UVA irradiation. The Raman spectroscopy and surface functional group analysis results suggested that (•)OH initially reacted with the surface carboxylated carbonaceous fragments, resulting in their degradation or exfoliation. Further reaction between (•)OH and the graphitic sidewall led to formation of defects including functional groups and vacancies. These reactions reduced the surface potential and colloidal stability of COOH-MWCNTs, and are expected to reduce their mobility in aquatic systems.

Behaviour of fullerenes (C60) in the terrestrial environment: potential release from biosolids-amended soils

Owing of their wide-range of commercial applications, fullerene (C60) nanoparticles, are likely to reach environments through the application of treated sludge (biosolids) from wastewater treatment plants to soils. We examined the release behaviour of C60 from contaminated biosolids added to soils with varying physicochemical characteristics. Incubation studies were carried out in the dark for up to 24 weeks, by adding biosolids spiked (1.5mg/kg) with three forms of C60 (suspended in water, in humic acid, and precipitated/particulate) to six contrasting soils. Leaching of different biosolids+soil systems showed that only small fractions of C60 (<5% of applied amount) were released, depending on incubation time and soil properties (particularly dissolved organic carbon content). Release of C60 from unamended soils was greater (at least twice as much) than from biosolids-amended soils. The form of C60 used to spike the biosolids had no significant effect on the release of C60 from the different systems. Contact time of C60 in these systems only slightly increased the apparent release up to 8 weeks, followed by a decrease to 24 weeks. Mass balance analysis at the completion of the experiment revealed that 20-60% of the initial C60 applied could not be accounted for in these systems; the reasons for this are discussed.

Dispersing carbon-based nanomaterials in aqueous phase by graphene oxides

Graphene oxides (GO) can be considered as polyelectrolytes with surfactant-like characteristics. On one hand, due to the electrical repulsion between the negatively charged ionized edges, GO exhibits great water solubility; on the other hand, its hydrophobic central plane retains the potential of strong π-π interaction with other conjugated sp(2) network structures. Therefore, it is expected that GO can serve as an excellent dispersing agent for dispersion of various carbon-based nanomaterials in aqueous phase. Here we report a systematic study of dispersing various carbon-based nanomaterials, including SWNTs, C60, and graphene, by aqueous GO. The GO-dispersed all-carbon nanocomposites are characterized using various spectroscopic methods and electron microscopies, and their stabilities are tested. Compared to other dispersing agents, the GO concentration is much lower than the concentrations of other dispersing agents used when similar contents of carbon-based nanomaterials are dispersed. Involving only simple ultrasonication and centrifugation processes, GO dispersion thus offers an easy manipulation for large-scale solution-dispersed all-carbon nanocomposites.

Quenching and sensitizing fullerene photoreactions by natural organic matter

Effects of natural organic matter (NOM) on the photoreaction kinetics of fullerenes (i.e., C60 and fullerenol) were investigated using simulated sunlight and monochromatic radiation (365 nm). NOM from several sources quenched (slowed) the photoreaction of C60 aggregates in water (aqu/nC60), but sensitized (accelerated) photoreaction of fullerenol. Kinetic studies indicated that the quenching occurred through a static mechanism involving NOM molecules adsorbed on the aqu/nC60 surface. Quenching constants for the photoreaction of aqu/nC60 correlated approximately with optical parameters related to the aromaticity and molecular size of the NOM. Association of aqu/nC60 particles with NOM was investigated indirectly via the study of the aggregation kinetics of colloidal C60 in the presence and absence of NOM as a function of NaCl strength at pH 7. In contrast to aqu/nC60, the photoreaction efficiencies of the hydrophilic fullerene, fullerenol, increased linearly with increasing NOM concentrations and kinetic parameters for the sensitized photoreactions increased as the spectral slope coefficients and ratio of absorption coefficients at 254 to 365 nm (E2:E3) of the NOM increased. The results indicate that triplet excited states of the NOM are key intermediates in the photosensitized reactions.

Contaminant-mobilizing capability of fullerene nanoparticles (nC60): Effect of solvent-exchange process in nC60 formation

Fullerene nanoparticles (nC(60)) in aqueous environments can significantly enhance the transport of hydrophobic organic contaminants by serving as a contaminant carrier. In the present study, the authors examine the effect of the solvent-exchange process on nC(60) aggregate formation and, subsequently, on nC(60) 's contaminant-mobilizing capability. A series of nC(60) samples were prepared using a modified toluene-water solvent-exchange method through the inclusion of a secondary organic solvent in the phase transfer of molecular C(60) in toluene to nC(60) in water. Two groups of solvents--a water-miscible group and a non-water-miscible group-of varied polarity were selected as secondary solvents. The involvement of a secondary solvent in the phase transfer process had only small effects on the particle size and distribution, ζ potential, and mobility of the nC(60) products but significantly influenced the capability of nC(60) to enhance the transport of 2,2',5,5'-polychlorinated biphenyl (PCB) in a saturated sandy soil column, regardless of whether the secondary solvent was water-miscible or non-water-miscible. The two groups of secondary solvents appear to affect the aggregation properties of nC(60) in water via different mechanisms. In general, nC(60) products made with a secondary water-miscible solvent have stronger capabilities to enhance PCB transport. Taken together, the results indicate that according to formation conditions and solvent constituents, nC(60) will vary significantly in its interactions with organic contaminants, specifically as related to adsorption or desorption as well as transport in porous media.

Enhanced transport of 2,2',5,5'-polychlorinated biphenyl by natural organic matter (NOM) and surfactant-modified fullerene nanoparticles (nC60)

Stable colloidal suspensions of buckminsterfullerene (nC(60)) in aqueous environments can significantly affect the fate and transport of hydrophobic organic contaminants by serving as a contaminant carrier. In this study, we examined enhanced transport of 2,2',5,5'-polychlorinated biphenyl (PCB) in saturated sandy soil columns by a variety of nC(60) samples, including an nC(60) sample prepared by the typical solvent exchange method, as well as eight natural organic matter (NOM) or surfactant-modified nC(60) samples, prepared by phase-transferring C(60) from toluene to an NOM or a surfactant solution. Whereas the NOM- and surfactant-modified nC(60) samples have mobility similar to the unmodified nC(60), their contaminant-mobilizing capabilities are significantly greater: breakthrough of PCB increases by 47.2 to 227% with the surfactant-modified nC(60) samples and by 233 to 370% with the NOM-modified nC(60) samples. The significantly enhanced contaminant-mobilizing capability of the modified nC(60) is likely due to a combined effect of increased adsorption affinities and increased tendency of desorption nonequilibrium, likely caused by the changes of nC(60) aggregation properties induced by the presence of NOM or surfactant. Findings in this study indicate that nC(60) formed in different processes might have vastly different effects on contaminant fate and transport.

Comparison of the cytotoxic responses of Escherichia coli (E. coli) AMC 198 to different fullerene suspensions (nC60)

Fullerenes are set to be produced on an industrial scale in anticipation of their wide applications. This calls for research on their environmental and health impacts. This study investigates and compares the cell toxicity of different aqueous fullerene aggregates. Popular C(60) dispersal methods were used to prepare four types of nC(60) aggregates. These aggregates were tested against the indicator species Escherichia coli (E. coli) AMC 198. With aggregates of around 150 nm in diameter, the THF/nC(60) suspension was very toxic and gave rise to a half maximal effective concentration (EC(50)) of 0.54 mg L(-1) in E. coli. By contrast, the Tol/nC(60) suspension exhibited a cytoprotective role while the Aqu-N(2)/nC(60) and Aqu-O(2)/nC(60) suspensions enhanced the metabolism of E. coli. Although some toxicants, such as THF and THF-peroxide, were introduced into the THF/nC(60) suspension during the dispersion, the toxicity of nC(60) itself cannot be neglected.

UV-vis spectroscopic properties of nC60 produced via extended mixing

Colloidally stable C(60) suspensions produced via extended mixing in water (aq/nC(60)) are highly heterogeneous with respect to particle size and morphology. Ultraviolet-visible (UV-vis) absorption spectra of aq/nC(60) are often used as a supplemental tool to dynamic light scattering (DLS), transmission electron microscopy (TEM), and other analytical methods to characterize aq/nC(60). In the present study, the UV-vis spectra provide information about the average particle size and the interactions between C(60) and water. We report that the decrease in relative absorption in the 240-290 nm range is a function of magnetic stirring time, that the average size (Z(ave)) of an aq/nC(60) suspension determines the position of absorbance maximum of its 360 nm band, and that the methods used to prepare and fractionate nC(60) affect the extent of the blue shift in this band that occurs due to a decrease in Z(ave). We also confirm that the broad absorption band in the 400-600 nm region is a result of C(60) aggregation.

Escherichia coli Inactivation by UVC-Irradiated C60: kinetics and mechanisms

Motivated by recent studies that documented changes in fullerene toxicity after chemical transformation, C(60) aggregates (nC(60)) were subject to UVC irradiation at monochromatic 254 nm and subsequently evaluated for antibacterial and bactericidal properties against Escherichia coli. The nC(60) treated with UVC irradiation, referred to herein as UVC-irradiated C(60), did not directly inhibit bacterial growth at concentrations up to 20 mg/L. In the presence of UVA and visible light, however, UVC-irradiated C(60) rapidly inactivated E. coli, suggesting that photochemical production of reactive oxygen species (ROS) was involved. The use of ROS scavengers and probes determined that hydroxyl radicals were the primary ROS responsible for the E. coli inactivation. Results from protein release, lipid peroxidation, cell permeability, and intracellular enzyme assays suggest that the inactivation mechanism involves UVC-irradiated C(60) diffusing through E. coli cell membrane and producing hydroxyl radicals within the cell. Further study on water-soluble C(60) derivatives and possible transformative processes is, therefore, recommended based on the environmental implications of results presented herein that nC(60) exposed to UVC irradiation is more toxic than parent nC(60).

Quantifying summed fullerene nC60 and related transformation products in water using LC LTQ Orbitrap MS and application to environmental samples

The application of engineered nanomaterials increases strongly. Development of analytical techniques and their application to environmental samples is essential for human and environmental risk assessment of the nanoparticles. The objective of this study was to develop a sensitive analytical method to quantify nC(60) in water, using accurate mass screening liquid chromatography-hybrid linear ion trap Orbitrap mass spectrometry. nC(60) can be transformed by oxidation, reduction and photochemical reaction. Therefore, the formation of some transformation products of nC(60) was studied as well. Finally, the developed analytical method was applied to surface water samples from several locations in the Netherlands. The developed method enabled to detect and quantify aqueous concentrations of the summed nC(60) and its transformation products as low as 5 ng/L. It was observed that nC(60) transformation products exceed quantities of the parent C(60). Despite the high sensitivity of the developed method, no nC(60) or transformation products were detected in an array of Dutch surface waters. This might be due to low emissions, losses in the aqueous phase by sedimentation, sorption or further transformation processes.

Aqueous fullerene aggregates (nC60) generate minimal reactive oxygen species and are of low toxicity in fish: a revision of previous reports

This review aims to clarify inconsistencies in previous reports regarding the potential for aqueous aggregates of fullerenes (nC60) to generate reactive oxygen species (ROS) and cause toxicity in fish. Methods for evaluation of ROS production and toxicity of aqueous nC60 have evolved over time and limitations in initial studies have led to unintentional erroneous reports of nC60 ROS generation and toxicity. Some of these reports continue to lead to misconceptions of the environmental effects of C60. Critical review of the evidence (2007-2011) indicates that aqueous nC60 have minimal potential to produce ROS and that oxidative stress in fish is not induced by environmentally relevant exposure to nC60. Future studies should acknowledge that current evidence indicates low toxicity of nC60 and refrain from citing articles that attribute toxicity in fish to nC60 based on methods shown to be compromised by experimental artifacts. Despite low toxicity of nC60 in fish, an emerging environmental issue is that nC60 can affect environmental fate, transport, and bioavailability of co-contaminants in aquatic environments in a similar manner to that observed for other anthropogenic particulates (e.g., microplastics).

The role of atmospheric transformations in determining environmental impacts of carbonaceous nanoparticles

In studies that have explored the potential environmental impacts of manufactured nanomaterials, the atmosphere has largely been viewed as an inert setting that acts merely as a route for inhalation exposure. Manufactured nanomaterials will enter the atmosphere during production, use, and disposal, and rather than simply being transported, airborne nanoparticles are in fact subject to physical and chemical transformations that could modify their fate, transport, bioavailability, and toxicity once they deposit to aqueous and terrestrial ecosystems. The objective of this paper is to review the factors affecting carbonaceous nanomaterials' behavior in the environment and to show that atmospheric transformations, often overlooked, have the potential to alter nanoparticles' physical and chemical properties and thus influence their environmental fate and impact. Atmospheric processing of naturally occurring and incidental nanoparticles takes place through coagulation, condensation, and oxidation; these phenomena are expected to affect manufactured nanoparticles as well. It is likely that carbonaceous nanomaterials in the atmosphere will be oxidized, effectively functionalizing them. By influencing size, shape, and surface chemistry, atmospheric transformations have the potential to affect a variety of nanoparticle-environment interactions, including solubility, interaction with natural surfactants, deposition to porous media, and ecotoxicity. Potential directions for future research are suggested to address the current lack of information surrounding atmospheric transformations of engineered nanomaterials.

Visible light sensitized inactivation of MS-2 bacteriophage by a cationic amine-functionalized C60 derivative

Recently, we reported the successful synthesis of various hexakis C60 derivatives (i.e., C60 with six functional groups containing NH3+-, CO2H-, or OH-terminals) with enhanced stability in water for aqueous phase application (Lee et al., Environ. Sci. Technol. 2009, 43, pp 6604-6610). Among these newly synthesized C60 derivatives, the cationic hexakis C60 derivative with amine functionality, C60(CR2)6 (R=CO2(CH2)2NH3+CF3CO2-), was found to exhibit remarkable efficiency to inactivate Escherichia coli and MS-2 bacteriophage under UVA irradiation. Herein, we report that this amine-functionalized C60 derivative is also photoactive in response to visible light from both commercial fluorescence lamps and sunlight. Efficient production of 1O2, facile reaction of 1O2 with proteins in MS-2 phage capsid and electrostatic attraction between positively charged C60 derivative and negatively charged MS-2 phage collectively contributed to high efficiency of MS-2 phage inactivation in this photocatalytic disinfection system. The rate of 1O2 production was evaluated using a probe compound, furfuryl alcohol, and 1O2 CT (the product of 1O2 concentration and exposure time) required to achieve a target level of virus inactivation was quantitatively analyzed. The unique visible-light sensitized virucidal property makes this C60 derivative highly desirable for the development of sustainable disinfection strategies that do not require continuous chemical addition nor an external energy source other than ambient light.

Evaluation of perfused porcine skin as a model system to quantitate tissue distribution of fullerene nanoparticles

Nanomaterials are increasingly playing a role in society for uses ranging from biomedicine to microelectronics, however pharmacokinetic studies, which will be necessary for human health risk assessments, are limited. Tissue distribution, one component of pharmacokinetics, can be assessed by quantifying arterial extraction of materials in an isolated perfused porcine skin flap (IPPSF). The objective of this study was to assess the IPPSF as a model system to quantitate the distribution of fullerene nanoparticles (nC(60)) from the vascular space into tissues. IPPSFs were perfused for 4h with 0.885 microg/mL nC(60) in media with immunoglobulin G present (IgG(+)) or absent (IgG(-)) followed by a 4h perfusion with media only during a washout phase. Arterial and venous concentrations of nC(60) were measured in the media by HPLC-UV/vis chromatography. Steady state differences in the arterial and venous nC(60) concentrations were compared to determine extraction from the vascular space of the IPPSF, and the venous nC(60) concentration versus time profiles were used to calculate compartmental pharmacokinetic parameters. The steady state differences in the arterial and venous concentrations in the IPPSF were small with extraction percentages (mean+/-sd) of 8.2+/-5.7% and 4.2+/-6.7% for IgG(+) and IgG(-) media, respectively, and were not significantly different between the types of media. The venous concentrations of nC(60) in both types of media were best fit with a 2 compartment model with terminal half lives (harmonic mean) of 17.5 and 28.0 min for IgG(+) and IgG(-) media, respectively. The apparent volumes of distribution at steady state were 0.12+/-0.047 and 0.10+/-0.034 L/kg, for IgG(+) and IgG(-) media, respectively. By 4 h following infusion of nC(60), the recovery of nC(60) in the venous effluent was 94+/-5.5% and 97+/-6.8% of the infused nC(60) for IgG(+) and IgG(-) media, respectively. Based on the apparent volume of distribution, the low extraction during the perfusion, and the high percentage recovery following the washout phase, there was limited distribution of nC(60) from the vascular space into the extracellular space and negligible intracellular uptake of nC(60) in this system.

Translocation of C(60) from aqueous stable colloidal aggregates into surfactant micelles

C(60)'s unique property of forming stable aggregates (nC(60)) in water, despite its exceedingly low aqueous solubility, has been linked to the potential for transport in the environment and exposure to biological receptors. The reversibility of aggregate formation could be an equally important parameter in understanding the ultimate fate of C(60), including accumulation in nonaqueous environments such as biological membranes, micellular phases, and the organic fraction of soils. This study suggests that C(60) molecules in nC(60) readily translocate into nonionic surfactant micelles, a commonly used surrogate for biological membranes. Upon contact with surfactant micelles, the restoration of C(60)'s photochemical reactivity was observed; i.e., efficient production of reactive oxygen species (ROS) such as singlet oxygen upon UVA irradiation. Further evidence to support C(60)'s spontaneous translocation from colloidal aggregates into surfactant micelles is provided, including UV-vis spectral change, visual observation via transmission electron microscope, change in the fluorescence of surfactant micelles, and a reduction in the particle size of the parent nC(60). Experiments performed with Escherichia coli also showed that singlet oxygen was produced when E. coli was in contact with nC(60), resulting in peroxidation of lipids. These findings collectively suggest that micelle/lipid systems could be one of the receptors of C(60) in the environment and provide insights into the previous observations of ROS production in biological systems exposed to nC(60).

Escherichia coli inactivation by water-soluble, ozonated C60 derivative: kinetics and mechanisms

Antibacterial and bactericidal effects of a C60 derivative prepared via excess ozonation of C60 aggregates in water were investigated using Escherichia coli as a representative microorganism. Ozonated C60 up to 10 mg/L did not cause significant growth inhibition nor inactivation of E. coli in the absence of either oxygen or light. However, it readily inactivated E. coli in the presence of both oxygen and light at much faster rate than parent C60 aggregates, suggesting involvement of photochemical generation of reactive oxygen species (ROS). Among ROS, hydroxyl radical was found as a primary agent for the cell inactivation. Little surface protein release and concurrent intercellular enzyme degradation during the course of E. coli inactivation, along with visual evidence obtained from transmission electron microscopic analysis, collectively indicated that the mechanism of E. coli inactivation by ozonated C60 involves efficient penetration of ozonated C60 into E. coli and subsequent photochemical production of hydroxyl radical within the cell cytoplasm. These findings suggest that oxidative transformation of C60 can lead to increased toxicity in addition to increased water solubility and reduced size, warranting further studies on other potential chemical derivatization possible in natural and engineered environments for an accurate assessment of environmental impact of this class of materials.

Photochemical and antimicrobial properties of novel C60 derivatives in aqueous systems

Four novel hexakis C60 derivatives with varying functionalities were synthesized, and their photochemical properties and photodynamic disinfection efficiencies were quantitatively evaluated. All these C. derivatives generated O2 more efficiently than commercial multihydroxylated C60 (fullerol), as assessed by furfuryl alcohol consumption and electron paramagnetic resonance analysis. Despite significant agglomeration/aggregation in the aqueous phase to micrometer-sized particles, nanosecond laser flash photolysis showed that the lifetime of triplet state (a key intermediate for energy transfer responsible for (1)O2 production) was comparable to reported values for pristine C. in organic phase. As a result of facile (1)O2 production, the Co derivatives efficiently inactivated Escherichie coli and MS-2 bacteriophage. Cationic aminofullerene hexakis, which likely exerted electrostatic attraction, exhibited exceptionally rapid virus inactivation even compared to commercial nano-TiO2 photocatalyst These unique photodynamic, hydrophilic and cationic properties may be instrumental for the development of next generation photocatalysts for disinfection applications. The high ROS (reactive oxygen species) production activity and associated cytotoxicity are concerns for potential releases of functionalized Ca to the environment, and require careful assessment apart from other forms of C60 (e.g., nC60) that have been widely studied as model nanomaterials but behave differently.

Transformation of aggregated C60 in the aqueous phase by UV irradiation

This study demonstrates that water-stable C60 cluster (nC60) undergoes a photochemical transformation(s) when irradiated with monochromatic UV light at 254 nm. Upon UV exposure, characteristic absorption of nC60 in the visible (ca. 450-550 nm, indicative of a cluster structure) and UV regions (indicative of underivatized molecular C60) gradually disappeared. Concurrently, a new product with absorption centered at 210 nm formed. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) analyses confirmed a complete reduction in aggregation and formation of a soluble product. Negligible loss of total organic carbon (TOC) and drastic retardation in degradation kinetics in the absence of oxygen collectively implied that photochemical transformation was accomplished via oxidative pathway without carbon mineralization. MS (LDI), FTIR, and XPS analyses indicated a 60 carbon cage product, containing various oxygen functional groups such as epoxides and ethers. In addition, this product demonstrated significantly less antibacterial effects on Escherichia coli when compared to the parent nC60. The results of this study suggest that accurate assessment of C60 in environmental life cycles and impact should consider the light-mediated transformation of C60 in the aqueous phase and resulting water-soluble products.

Lipid-assisted formation and dispersion of aqueous and bilayer-embedded nano-C60

Lipid assemblies provide a biocompatible approach for preparing aqueous nanoparticles. In this work, dipalmitoylphosphatidylcholine (DPPC) was used to assist in the formation and dispersion of C(60) and nano-C(60) aggregates using a modified reverse phase evaporation (REV) method. This method led to the rapid formation of aqueous nano-C(60) at DPPC/C(60) molar ratios from 500:1 to 100:1 (12-38 nm; verified by cryogenic transmission electron microscopy), which were present in the bulk phase and encapsulated within vesicles. In addition to forming nanoparticles, C(60) was trapped within the vesicle bilayer and led to a reduction in the lipid melting temperature. Solvent extraction was used to isolate nano-C(60) from the lipids and bilayer-embedded C(60). Our results suggest that bilayer-embedded C(60) was present as molecular C(60) and as small amorphous nano-C(60) (2.3 +/- 0.4 nm), which clustered in the aqueous phase after the lipids were extracted. In addition to developing a new technique for nano-C(60) formation, our results suggest that the lipid bilayer may be used as a hydrophobic region for dispersing and assembling small nano-C(60).